Excess water seriously
affects the performance and lifetime of
proton exchange membrane fuel cells (PEMFCs). This study proposes
a novel compound flow field, which is named the active drainage flow
field (ADFF). The new design enhances the drainage performance by
under-ribs flow, while the output performance is very close to that
of the conventional serpentine flow field (CSFF). Additionally, the
ADFF bipolar plate has been taken as a cathode while retaining CSFF
as an anode; the combination shows a good output performance under
high relative humidity. The peak power density has reached to 0.59
W/cm
2
, which is 13% higher than that of the CSFF.
In this paper, a method to improve the performance of PEMFCs using porous material as a flow channel baffle is proposed. The results show that PEMFCs with four porous baffles flow channels have better performance at high current density compared with the traditional flow channel. The structural parameters of the flow channel explored in this study include porosity, the thickness of the baffle and the number of baffles, and their influence on the performance of PEMFCs. Sensitivity analysis results show that the performance of the PEMFCs with the porous baffle channel is the most sensitive to baffle thickness, and the thickness and baffle could be appropriately adjusted. The number of plates and porosity of the baffle are adjusted to improve the performance of the PEMFCs.
Graphite is expected to be a common choice for basic microelectromechanical-system (MEMS) material in the future. However, in order to become a basic MEMS material, it is very important for graphite to be adapted to the commonly-used micro-/nanoprocessing technology. Therefore, this paper used a directly lithography and etching process to study micro-, /nanoprocessing on graphite. The results show that the graphite surface is suitable for lithography, and that different shapes and sizes of photoresist patterns can be directly fabricated on the graphite surface. In addition, the micro-meter height of photoresist could still resist plasma etching when process nanometers height of graphite structures. Therefore, graphite with photoresist patterns were directly processed by etching, and nanometer amounts of graphite were etched. Moreover, micro-/nanoscale graphite structure with height ranges from 29.4 nm–30.9 nm were fabricated with about 23° sidewall.
Water management in proton exchange membrane fuel cells (PEMFC) is a topic of great importance for the optimization of these systems. Effective proton conductivity calls for moderate moisture content in the membrane, while uneven water distribution can lead to instability of the whole flow field, thereby decreasing the performance of the fuel cell. In the present study, a simplified two-tier hybrid structure is used to investigate the impact of the dynamic behavior of liquid water on the current density of the PEMFC. Simulation results show that water droplets attached to wall sides tend to increase current density. Visualization experiments confirm the existence of liquid droplets and the enhancement of current density, while indicating that the best performance and stability of fuel cell are attained for a cathode air flow rate of 300 ml/min.
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